Millions of trees die in California drought, adding to fire danger

New growth is seen alongside damage caused by the 2013 Rim Fire in the Stanislaus National Forest in California

New growth is seen alongside damage caused by the 2013 Rim Fire in the Stanislaus National Forest in California May 30, 2014. REUTERS/Elijah Nouvelage

SACRAMENTO, Calif. (Reuters) - California's drought led to the deaths of 12.5 million trees in the state's forests last year, leaving behind huge amounts of dry fuel that could burn easily as the summer wildfire season begins, the U.S. Forest Service said Monday.

The dead trees, visible from the air as red patches in the forest, were weakened by drought and in many cases then killed by bark beetles, which have infested the state's forests and thrive in the warm, dry conditions.

"In some places, we had 100 percent mortality," said Jeffrey Moore, a biological scientist with the Forest Service whose team mapped the dead trees by airplane last month.

The Forest Service report, which was released on Monday, included aerial surveys of about 8.3 million acres throughout the state.

The Forest Service has been closely tracking tree deaths since the start of the drought, now in its fourth year.

The dry weather has made conifers in the state's wooded area particularly vulnerable to beetles, which attack when the trees are weak, eventually killing them.

Stanton Floria, a spokesman for the Forest Service, said the drought was a major factor driving forest fires last year, and dry weather and dead trees and brush will exacerbate blazes again this summer.